1. Field of the Invention
This invention relates to a method for the visualization of fluid flows over the surfaces of solid components at elevated temperatures. A smear caused by fluid flow across the surface of the substrate is indicative of the direction and/or speed of flow.
2. Description of the Prior Art
It is known to apply a coating, with non-geling characteristics, to a surface of a component which on the subsequent passage of a fluid flow thereover will move to produce a visible pattern of streaks in the coated surface. The pattern generated in the coating enables visualization of the fluid flow direction across the component surfaces.
According to the invention disclosed in U.S. Pat. No. 4,915,975 to Watson, for example, a method of fluid flow visualization comprises the steps of coating a component with a pigmented oil based paint of non-geling characteristics, applying dry dye particles which are soluble in the oil based paint to the surface of the coating and passing a fluid flow over the component, whereby the fluid flow causes the dye particles to translate across the coating dissolving to leave trails on the surface of the coating, which trails enable visualization of the passage of the fluid flow over the surface of the component. In that patent, the pigmented oil based paint preferably comprises a solid solution of a fluorescent pigment in a melamine formaldehyde sulphonamide resin suspended in a mineral oil. Also, the pigmented oil based paint preferably includes a wetting agent such as linoleic acid, and the dry dye particles applied to the coating of pigmented oil based paint are preferably of a contrasting phthalocyanine dye.
In U.S. Pat. No. 4,774,835 to Holmes et al., a liquid crystal coating has been formulated for use in aerodynamic or hydrodynamic testing, to change colors in response to differences in relative shear stress within the temperature environment of a test object. This liquid crystal coating is then applied to the surface of the test object, and the test object is subjected to a liquid or gas flow either in flight or in a wind or water tunnel. By recording and measuring the color changes produced within the boundary layer surrounding the surface of the test object, transition locations and modes are observed as well as such aerodynamic phenomena as shock locations and laminar separation bubbles.
U.S. Pat. No. 3,301,046 to Rubert et al. relates generally to a method of obtaining a permanent record of surface flow phenomena for future study and relates with particularity to a method of producing a mold of the surface flow pattern observed on a wind tunnel test model, when employing the oil-smear indicating technique, and displaying this mold in such manner as to permit photographic permanent recordation of the surface flow pattern obtained. According to that invention, a mixture of oil and lampblack is applied to selected areas of a specific wind tunnel test model. The test model is subjected to a specific wind tunnel test; and, after completion of the test, the wind tunnel is shut down, the model removed and a film of liquid room-temperature vulcanizable elastomeric material is applied over the entire model test surface area and permitted to cure. As the elastomeric material cures, it completely absorbs the oil smear on the test model and retains every minute detail of the surface flow pattern as indicated by these oil smears. After curing, the film of flexible elastomeric material is stripped from the test model to provide a pattern of the surface flow which may then be displayed for suitable photographing and permanent recordation thereof.
Another pertinent prior art reference is U.S. Pat. No. 3,415,122 to Yee which discloses a temperature indicator in the form of a ceramic film for sensing and recording temperatures in the range of 900.degree. C.-1400.degree. C. The film may be attached, for example, to the outer skin of a space vehicle. When recovered after re-entry of the space vehicle, the indicator is cleaned, polished, and photomicrographed, then compared with calibration photomicrographs to determine the maximum temperature to which the space vehicle was subjected.